the control of gene expression

Question 1

Describe substitution

Answer 1

one nucleotide is replaced by another with different base

Question 2

describe deletion

Answer 2

loss of a nucleotide base from the DNA sequence, causes a frameshift

Question 3

describe addition

Answer 3

addition of a nucleotide base in a sequence, causes a frameshift

Question 4

describe duplication

Answer 4

one or more bases repeated, causes a frame shift
Inversion: sequence of bases separated from the DNA sequence and then reattach in the same place but the opposite order

Question 5

describe translocation

Answer 5

group of bases separated from the DNA sequence on one chromosome and inserted into the DNA sequence on a different chromosome

Question 6

Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - substitution

Answer 6

the substituted base may produce a stop codon, a codon coding for a different amino acid or a codon coding for the same amino acid

Question 7

Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - deletion

Answer 7

causes a frameshift. All bases following the substitution shifted to the left causing remaining to codons to be different and potentially code for different amino acids

Question 8

Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - addition

Answer 8

causes a frameshift. All bases following the substitution shifted to the right causing remaining to codons to be different and potentially code for different amino acids

Question 9

Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - duplication

Answer 9

causes a frame shift to the right

Question 10

Explain how the different types of gene mutation result in different amino acid sequences in polypeptides - inversion

Answer 10

amino acid sequence in the area of inversion affected

Question 11

Explain why some mutations do not result in a changed amino acid sequence

Answer 11

-Different codon coding for the same amino acid may be formed
-this will have no effect on the protein formed.
-This occurs because the genetic code is degenerate

Question 12

Discuss the causes of gene mutations

Answer 12

-Natural mutation rate (spontaneous mutation) is 1 mutation per 100 000 genes per generation.
-Mutagenic agents increase this rate:
High energy ionising radiation: eg alpha and beta radiation, x rays, UV light.
Chemicals: eg nitrogen dioxide alters DNA structure of interferes with transcription

Question 13

State what totipotent cells are

Answer 13

Totipotent cells can develop into any types of cell, eg fertilised egg

Question 14

Explain how cells lose their totipotency and become specialised

Answer 14

-During specialisation only some genes are expressed
-so the cell only makes the proteins it needs to carry out its specialised function.
-A variety of stimuli ensure that the genes that are not needed stay switched off.

Question 15

Describe cell differentiation and cell specialisation

Answer 15

-Cell differentiation: process by which cells develop into specialised cells.
-No one cell can provide the best conditions for all functions.
-More efficient if they are adapted to their function

Question 16

Describe the origins and types of stem cells

Answer 16

-Totipotent: in early embryo – develop into any type of cell. Zygote is totipotent. It develops into …
-Pluripotent: in embryos – become almost any type of cell. Eg embryonic and foetal stem cells
-Multipotent: in adults – differentiate into a limited number of specialised cells. Eg bone marrow make blood cells. Eg of -multipotent – adult stem cells, umbilical cord stem cells.
-Unipotent: differentiate into single type of cell – derived from multipotent cells and found in adult tissue”

Question 17

Explain how pluripotent stem cells can be used to treat human disorders

Answer 17

-Cells can be used to regrow tissues that have been damaged:
Skin grafts for burns. Heart muscle cells for heart damage,
Nerve cells for MS, spinal injury etc Blood cells for leukaemia, Bone cells for osteoporosis, Retina cells for macular degeneration

Question 18

State what is meant by epigenetics

Answer 18

Heritable changes in gene function due to environmental factors that do not change the base sequence of DNA

Question 19

Describe the nature of the epigenome

Answer 19

-The epigenome is a series of chemical tags attached to DNA and histones that affects the transcription of DNA

Question 20

Explain the effect of epigenetic factors on DNA and histones

Answer 20

-The epigenome determines the shape of the DNA-histone complex by changing how tightly wrapped the DNA is.
-When tightly wrapped the DNA cannot be transcribed,
-when loosely coiled DNA can be transcribed

Question 21

Explain the effects of decreased acetylation of histones

Answer 21

-Gene switched off (inactive):
-Decreased acetylation of histones
-Increased positive charges on histones which increases attraction to phosphate groups on DNA
-Genes tightly packed (condensed)
-Transcriptional factors cannot bind
-Transcription cannot occur so mRNA is not made
-Protein is not produced

Question 22

Explain the effects of increased methylation of DNA

Answer 22

-Gene switched off (inactive):
-Increased methylation of DNA
-Prevent binding of transcriptional factors to DNA
-Attract proteins that condense DNA/histone complex by inducing deacetylation
-Genes tightly packed (condensed)
-Transcriptional factors cannot bind
-Transcription cannot occur so mRNA is not made
- Protein is not produced

Question 23

Distinguish between benign and malignant tumours

Answer 23

Benign tumours are not cancerous, malignant tumours are cancerous

Question 24

Explain the role of oncogenes and tumour suppressor genes in the development of tumours

Answer 24

-Oncogenes: mutations of proto-oncogenes > oncogenes are permanently activated and stimulate cell division causing tumours.
-Tumour suppressor genes: slow cell division> if mutated become inactive > and therefore cell division increases and tumours develop

Question 25

Explain the effects of abnormal methylation of tumour suppressor genes and oncogenes

Answer 25

-Abnormal methylation of tumour suppressor genes:
-hypermethylation in promotor region of tumour suppressor gene inactivates the gene and transcription is inhibited.
-Tumour suppressor gene no longer reduces cell division
-Abnormal methylation of oncogenes: hypomethylation leads to activation and increased cell division

Question 25

Explain how increased oestrogen levels can cause breast cancer

Answer 25

-Oestrogen causes transcription factors to become active and increase transcription,
-this can lead to increased cell division
-and therefore tumours if it acts on a gene that controls cell division.
-Oestrogen can also turn proto-oncogenes into oncogenes

Question 25

Discuss the determination of the genome and proteome of simple organisms

Answer 25

-Relatively easy as prokaryotes contain one circular piece of DNA, no histones, no non coding DNA.
-Can be used to identify proteins that act as antigens on pathogens in order to develop vaccines.

Question 25

Outline the importance of genome sequencing projects

Answer 25

-Mapping the entire human genome has resulted in identification of single nucleotide polymorphisms (SNPs) that are associated with disease - screening allows early identification and intervention to reduce potential medical problems
-Sequencing prokaryotes and single cell eukaryotes will help cure disease and provide knowledge of genes that can be usefully exploited

Question 25

Describe the nature of the proteome

Answer 25

The proteome is all of the proteins produced in a given cell/organism, at a given time, under specific conditions

Question 26

Discuss the determination of the the genome and proteome of complex organisms

Answer 26

-Challenging to translate the genome into a proteome as there are many areas of non coding DNA.
-and as all individuals are different whose DNA should be used to map the genome